1. Field of the Invention
The present invention relates to an organic electroluminescence display device which is used as a display device or a light source and which can be formed by a process including photolithography with easy isolation of organic electroluminescence elements, and also to a producing method of the above organic electroluminescence display device.
2. Description of the Related Art
At present, liquid crystal display devices are used as thin flat panel displays which are currently the main stream of the technical field of display devices. However, organic electroluminescence (hereinafter referred to "organic EL") display devices using organic EL elements are superior to liquid crystal display devices in the following points:
(1) Having a wide viewing angle because the organic EL elements emit light by themselves.
(2) Allowing easy manufacture of a thin display device of about 2-3 mm in thickness.
(3) Capable of providing a natural emission color because of no need for using any polarizing plate.
(4) Capable of clear display because of a wide light and shade dynamic range.
(5) Allowing organic EL elements to operate in a wide tenperature range.
(6) Easily enabling dynamic image display because the response speed of the organic EL elements is three orders or more higher than that of liquid crystal elements.
In spite of the above advantages, the organic EL display devices have the following problems in manufacture. For example, organic layers constituting the organic EL elements and electrodes containing a metal having a small work function which is usually used as a cathode to inject electrons into the organic layers are easily deteriorated by water and oxygen. Further, the organic layers are easily dissolved by a solvent and are not resistant to heat.
In a manufacturing method using water, organic solvents, and heat, it is difficult to isolate or divide elements after the formation of organic layers and an electrode containing a metal having a small work function. Therefore, when it is intended to form an organic EL display device in the same class as liquid crystal display devices currently implemented, the matured semiconductor manufacturing technology and liquid crystal display device manufacturing technology cannot be applied as they are to isolate small organic EL elements.
In the above circumstance, a method has been proposed in which walls higher than films constituting organic EL films are formed between display line electrodes to be isolated, and materials for forming the organic EL films are vacuum-evaporated in a direction not perpendicular to the substrate surface (i.e., evaporated obliquely). This method utilizes the fact that the materials for forming the organic EL films are not formed in the portions shielded by the high walls. (Refer to U.S. Pat. Nos. 5,276,380 and 5,294,869.)
In the above method, it is very important that the directions in which atoms or molecules travel from the evaporation source to the substrate be aligned. As shown in FIG. 8, in an ordinary evaporation method, an evaporation material is vaporized to assume concentric spheres with an evaporation source 101 in which the evaporation material is set as the center, and then attaches to a substrate 100. The incident angle of the evaporation material with respect to the substrate 100 varies with the position on the substrate 100, and the thickness of a resulting film formed on the substrate 100 varies in response to the distance from the evaporation source 101.
Therefore, it is difficult for the above method to isolate the display line electrodes in a stable manner, and to form the films uniformly over the entire substrate surface. Although the above method could manufacture small-size display devices, in order to apply the above method to medium-size or large-size substrates of the 10-inch class or larger, for example, the distance between the substrate 100 and the evaporation source 101 should be set sufficiently long. In this case, the size of the evaporation apparatus becomes impractical.
Even if such a large evaporation apparatus is produced, a large amount of organic EL material does not reach the substrate surface, and thus is consumed in vain without being formed on the substrate, resulting in a major factor of cost increase.
In general, a substrate is rotated or a plurality of evaporation sources are used to evaporate a thin film uniformly on the substrate. These methods are actually employed in semiconductor device manufacturing processes and liquid crystal device manufacturing processes. However, if the above method of forming high walls is applied to these methods, the element isolation cannot be attained any more.
In the conventional method, the organic EL films and the metal electrodes having a small work function are necessarily exposed unless protecting layers are consecutively formed in the same direction. Thus, it is difficult to completely eliminate the influences of water, oxygen, etc. It is impossible to perform photolithography having a process using an organic solvent or water after formation of the organic EL films.